Modern irrigation systems have provided a benefit to many agricultural applications. One such application is shown in FIGS. 1 and 2. In the growing of orchard crops, an underground pipe 10 is disposed throughout the orchard to provide a source of water under pressure. Periodically, riser pipes 12 are connected to the underground pipe 10 and vertically disposed as shown in FIG. 1 between one or more trees 14 to be watered thereby. The vertical riser pipes 12 have a sprinkler head 16 disposed thereon of the type shown in FIG. 3. Each sprinkler head 16 has a cylindrical body portion 18 adapted on the bottom end for attachment to the riser pipe 12 and having a nozzle portion 20 extending vertically from the top thereof along the longitudinal axis 22. The cylindrical body portion 18 has a turbine motor (not shown) disposed therein such that as irrigation water 24 entering from riser pipe 12 passes therethrough, nozzle portion 20 is rotated horizontally about the longitudinal axis 22 whereby the water 24 emerges from a nozzle opening 26 as a stream 28 which stream soon disperses and, thereby, creates the horizontal spray pattern 30 shown as the cross-hatched area in FIG. 2. Frequently in such orchards, a sprinkler head 16 creating a 360.degree. spray pattern (i.e. a full circle) is placed between several trees 14 in the manner shown in FIG. 2. By using a sprinkler head 16 of the type creating a partial circular arc, one, two, or more trees 14 can also be watered, but such an approach would typically be more expensive and, therefore, unused.
While such sprinkler systems have afforded obvious benefits, certain orchard crops have also suffered detriment thereby. In particular, in such orchard crops as walnuts and almonds, the type of watering pattern necessary has also often created an associated problem of wood rot in conjunction with the crowns and roots of the trees.
Wood rotting diseases of particular concern to the walnut and almond orchard owners in California are Phytophthora (Crown Rot) and Poria. Crown Rot moves directly into and through live tissue and can open the door for Poria, a moisture loving organism that enters the dead, inner wood of the trunk and main roots. These diseases cause less production of almonds and walnuts, originally, and eventually to the loss of the infected tree. The problem is a growing one because of the trend towards permanent set sprinkler systems which, because of the need for frost protection, are commonly being designed with application rates as low as 0.065 inches per hour. This means that irrigation sets of up to 96 hours are necessary in the summer to satisfy the consumptive water use of the orchard, which, in turn, creates a humid environment suitable for fungi growth. From investigations made by the applicant herein, it appears that at least 50% of the walnut orchards in northern California, especially along the Sacramento River, are either experiencing Crown Rot now or have the potential for it. Over one-half of the 160 thousand acres of walnuts in California are in this area, with an annual crop value of over $1,000 per acre. In almonds, where it is estimated that 10-15% of the orchards are infested with Poria, the planted acres and permanent set systems are even larger, though the problem is not as severe. Over one hundred throusand acres of the nearly 270,000 acres planted in California are in this area. This means that over 10,000 acres of almonds, with approximately the same value per acre as walnuts, are either infected with, or have the potential for, Poria wood rot.
At present, there is no means for employing such sprinklers to irrigate such orchards without causing the wetting of the trunks of the tree at the same time. Wherefore, it is the object of the present invention to provide an improvement in such sprinkler systems to prevent the trunks of the trees from being maintained in a wet condition by the irrigation system, while, at the same time, providing full irrigation coverage to the area except for the trunks of the trees per se.